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**Statistical **Physics Seminar

Tuesday, February 29, 2000, 1:15 p.m.

IPST Building, Room 1116
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*Quantum superconductor-insulator phase transition in ultrathin nanowires*

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Alexey Bezryadin

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(Harvard University)

**Abstract:** The phenomenon of superconductivity depends on the
coherence of the phase of the condensate. For small systems, such as Josephson
junctions or ultrathin wires, the phase is a quantum variable which may
or may not have a definite value, corresponding to superconducting and
insulating states respectively. To study these quantum effects in quasi-one-dimensional
superconductors we have developed a new technique which allows fabrication
of uniform nanowires down to ~5 nm in diameter. This is below the resolution
limit of modern electron beam lithography. Measurements on nanowires of
different sizes show that the insulating state does exist -- it occurs
in wires which have their normal-state resistance higher than the quantum
resistance for Cooper pairs. A superconducting state is recovered when
the "friction", given by the normal conductance of the wire, is strong
enough to suppress tunneling of phase slips.
**Host:** Ellen Williams

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